Enhanced touch-screen display system

ABSTRACT

An enhanced touch-screen display system is disclosed for generating pixel coordinate estimates corresponding to a location on a display screen touched by a user. The system is an analog resistive touch-screen display system having a processor and associated software algorithms to allow for the calibration and validation of pixel coordinate estimates as an integral part of the real-time generation of the pixel coordinate estimates. Multiple calibrated pixel coordinate estimates are generated and processed at a pre-defined sampling rate to determine a valid pixel position to minimize sampling delays due to settling times. The x-axis position is also validated before the system attempts to generate a y-axis position to avoid the wasted time for generating y-axis estimates when x-axis estimates are corrupted. Noisy estimates are inherently reduced in the touch-screen display system by providing shunts across certain drivers in the system that also allow for detection of a “no touch” state.

BACKGROUND OF THE INVENTION

[0001] This disclosed embodiment relates to a touch-screen displaysystem for generating pixel coordinate estimates responsive to a usertouching (pressing a key on) a display screen, and more particularlyrelates to improving the efficiency of generating such pixel coordinateestimates through enhanced techniques of calibration and validation ofthe estimates.

[0002] In a typical touch-screen display system, an x-axis coordinateposition is sampled and then a y-axis coordinate position is sampled toindicate a pixel location where a user has touched the display screen.If the samples are corrupted by noise or by drift of some parameter ofthe system, then these samples yield an incorrect indication of wherethe user has touched the display screen.

[0003] Typically, the system is controlled to insert timing delays intothe sampling process to allow the various x-axis and y-axis drivers tosettle out as they are switched back and forth between x and y so noisyestimates are avoided.

[0004] Calibration routines are typically run which require the user toassist in this calibration effort by touching various known locations onthe display screen and/or require implementing look-up tables andpre-calibrated cables in the system.

[0005] Also, in many touch-screen display systems, only an active touchof the display screen (or apparent touch caused by system noise) isdetected. Detecting the absence of a touch (key press) and reducing thepossibility of a false touch caused by noise is often just as desirableas detecting the position of an active touch.

[0006] U.S. Pat. No. 6,246,394 to Kalthoff et al. includes aconventional analog resistive touch-screen display assembly 2. Itemploys a 4-wire arrangement for taking measurements. U.S. Pat. No.6,016,140 to Blouin et al. is directed to a system and method that useslook-up tables and calibration cables for calibration. U.S. Pat. No.5,751,276 to Shih is directed to a method for calibrating touch paneldisplays using mapping transfer information. U.S. Pat. No. 5,241,139 toGungl et al. determines the position of a member contacting a touchscreen by tracking coordinates. U.S. Pat. No. 4,145,748 to Eichelbergeret al. includes a charge transfer analog-to-digital converter for adigital reading obtained for a “no touch” condition stored in memory,comparing digital readings from each pad to the “no touch” readingstored in memory.

[0007] An approach to generating pixel coordinate estimates thatminimizes sampling delays, reduces corruption of estimates due to noise,eliminates the need for user-interactive calibration, enhances ESDprotection, or provides more than one of these features is desired.

BRIEF SUMMARY OF THE INVENTION

[0008] One aspect of the disclosed embodiment is a calibratedtouch-screen display system for generating a pixel coordinate estimateresponsive to a user touching a display screen. In other words, thesystem detects that the screen has been touched, and determines“coordinates,” such as a vertical position and a horizontal position onthe screen, indicating where it has been touched.

[0009] “Pixels” are the elements or building blocks arranged on thescreen to display an image. The pixels may be displayed on, for example,an LCD display or other active display, or may be the coordinates offeatures on a passive display, such as a panel with permanent indiciaapplied to it.

[0010] Apparatus for calibrating the touch-screen display system isprovided. “Calibrating” means determining and correcting errors in theestimated coordinates, so the measured coordinates are accurate. Thisapparatus includes a processor that uses the digital signals it receivesfrom the touch-screen to produce calibrated pixel coordinate estimates.This calibration is performed during real-time generation of the pixelcoordinate estimates without the need for any extraordinary input by auser of the system. In other words, the calibrated estimates areproduced essentially at the same time the coordinate estimates areproduced, so the system automatically recalibrates itself as it is used.Automatic calibration reduces or eliminates the need for manualrecalibration.

[0011] Another aspect of the disclosed embodiment is an apparatus forgenerating and processing multiple calibrated pixel coordinate estimatesat a pre-defined sampling rate to determine valid pixel position inorder to minimize sampling delays due to settling times. The x-axisposition is validated before the system attempts to generate a y-axisposition so as not to waste time generating y-axis estimates when x-axisestimates are not valid. Shunts are designed in conjunction with thepre-defined sampling rate to establish pre-determined settling times(corresponding to discharge rates of capacitance on the analoginterfaces) such that voltage levels of the analog interfaces can besampled and processed by the system to indicate a “no touch” state ofthe system.

[0012] A method for calibrating the touch-screen display system isprovided. This method includes generating digital signals to producecalibrated pixel coordinate estimates. This calibration is performedduring real-time generation of the pixel coordinate estimates withoutthe need for any extraordinary input by a user of the system. In otherwords, the calibrated estimates are produced essentially at the sametime the coordinate estimates are produced, so the system automaticallyrecalibrates itself as it is used.

[0013] Another aspect of the disclosed embodiment is a method forgenerating and processing multiple calibrated pixel coordinate estimatesat a pre-defined sampling rate to determine valid pixel position inorder to minimize sampling delays due to settling times. The x-axisposition is validated before the system attempts to generate a y-axisposition so as not to waste time generating y-axis estimates when x-axisestimates are not valid. Noisy estimates are inherently reduced in thetouch-screen display system employing unique shunting techniques inconjunction with driving techniques in the system. These shuntingtechniques are used in conjunction with a pre-defined sampling rate toestablish predetermined settling times (corresponding to discharge ratesof capacitance on the analog interfaces) such that voltage levels onthese analog interfaces can be sampled and processed by the system toindicate a “no touch” state of the system.

[0014] By using the foregoing techniques, an approach to generatingpixel coordinate estimates that minimizes sampling delays, reducescorruption of estimates due to noise, enhances ESD protection, andeliminates the need for user-interactive calibration is achieved.

[0015] A further aspect of the invention is a method of determining atouch screen coordinate for a touch screen. The method comprises thesteps of: turning on the driver of the coordinate to be measured;measuring minimum, maximum, and raw position data for the coordinatebeing measured; and determining the coordinate position as a function ofthe raw position in relation to a coordinate range.

[0016] An additional aspect of the invention is an apparatus determininga touch screen coordinate for a touch screen. The apparatus comprises acontroller turning on the driver of the coordinate to be measured;circuitry on devices measuring minimum, maximum, and raw position datafor the coordinate being measured; and a controller determining thecoordinate position as a function of the raw position in relation to acoordinate range.

[0017] Yet another aspect of the invention is a method of determiningwhether or not a touch screen has been touched. The method comprises thesteps of: providing an analog to digital converter which supplies ananalog to digital reading; reading a minimum bit level; determiningwhether the reading is smaller than a minimum bit level; and determiningthe absence of a user touch if the reading is less than the minimum bitlevel.

[0018] Still another aspect of the invention is apparatus determiningwhether or not a touch screen has been touched. The apparatus comprisescircuitry providing an analog to digital reading from an analog todigital converter; a controller reading a minimum bit level; a computingelement determining whether the reading is smaller than the minimum bitlevel; and a controlling element determining the absence of a user touchif the modified reading is less than a minimum bit level.

[0019] A yet further aspect of the invention is a method of speeding upthe reading of analog to digital converter signals to a touch screen.The method comprises the steps of: reading a first coordinate of acoordinate pair at a first time; consecutively reading the samecoordinate at a second time; determining if the absolute value of thedifference between the first coordinate and the consecutive coordinateis less than a predetermined value; and quantifying, responsive to thedifference determining step the coordinate position as a function of thefirst or the consecutive coordinate.

[0020] A still further aspect of the invention is apparatus speeding upthe reading of analog to digital converter signals to a touch screen.The apparatus comprises circuitry reading a first coordinate of acoordinate pair at a first time; circuitry consecutively reading thesame coordinate at a second time; a controller element determining ifthe absolute value of the difference between the first coordinate andthe consecutive coordinate is less than a predetermined value; and acomputing element, response to the controller element quantifying thecoordinate position as a function of the first or the consecutivecoordinate.

[0021] A yet further aspect of the invention is a method of determiningwhether or not a touch screen has been touched. The method comprises thesteps of: reading a first coordinate of a coordinate pair at a firsttime; consecutively reading the same coordinate at a second time;determining if the absolute value of the difference between the firstcoordinate and the consecutive coordinate is less than a predeterminedvalue; and quantifying, responsive to the difference determining stepthe coordinate position as a function of the first or the consecutivecoordinate.

[0022] A still further aspect of the invention is apparatus determiningwhether or not a touch screen has been touched. The apparatus comprisescircuitry reading a first coordinate of a coordinate pair at a firsttime; circuitry consecutively reading the same coordinate at a secondtime; a controller element determining if the absolute value of thedifference between the first coordinate and the consecutive coordinateis less than a predetermined value; and a computing element, response tothe controller element quantifying the coordinate position as a functionof the first or the consecutive coordinate.

[0023] Another aspect of the invention is in an apparatus for enablingdetection of a “no touch” state of a touch-screen display system forgenerating pixel coordinate estimates responsive to a user touching adisplay screen. The touch-screen display system comprises: at least onebus bar; at least one driver electrically connected to said at least onebus bar to selectively switch the at least one bus bar between at leasttwo of a plurality of electrical potentials wherein the at least onedriver is selected to have an off state impedance establishing apre-determined discharge rate.

[0024] Yet another aspect of the invention is in an apparatus forenabling detection of a “no touch” state of a touch-screen displaysystem for generating pixel coordinate estimates responsive to a usertouching a display screen. The touch-screen display system comprises: atleast one bus bar; at least one driver electrically connected to said atleast one bus bar to selectively switch the at least one bus bar betweenat least two of a plurality of electrical potentials wherein the atleast one driver is controlled to establish pre-determined dischargerates.

[0025] Still another aspect of the invention is a method of determiningwhether or not a touch screen has been touched. The method comprises thesteps of: providing an analog to digital converter which supplies ananalog to digital reading; reading a maximum bit level; determiningwhether the reading is smaller than the maximum bit level; anddetermining the absence of a user touch if the modified reading is lessthan the maximum bit level.

[0026] An additional aspect of the invention is an apparatus determiningwhether or not a touch screen has been touched. The apparatus comprises:circuitry or the like providing an analog to digital reading from ananalog to digital converter; circuitry or the like reading a maximum bitlevel; circuitry or the like determining whether the reading is smallerthan the maximum bit level; and circuitry or the like determining theabsence of a user touch if the reading is less than a maximum bit level.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is a schematic block diagram of certain elements of thetouch-screen display system made in accordance with the disclosedembodiment, particularly showing the shunts and the 8-wire samplingconfiguration.

[0028]FIG. 2 is a schematic block diagram of the processor of thetouch-screen display system with certain associated software algorithmsincluding a validity algorithm, calibration algorithm, and correctionalgorithm. This processor interfaces to the elements in FIG. 1.

[0029]FIG. 3 is a flowchart of the calibration algorithm utilized by theprocessor shown in FIG. 2.

[0030]FIG. 4 is a flowchart of the validity algorithm utilized by theprocessor shown in FIG. 2.

[0031]FIG. 5 is a schematic block diagram of the active areas of thetouch screen display and analog resistive screens of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0032] The features of one embodiment enable improved efficiency ingenerating pixel coordinate estimates through enhanced techniques ofcalibration and validation of the estimates. As used in thisspecification and claims, a pixel coordinate estimate corresponds tothat pixel position on the touch-screen display that is an estimate ofwhere a user has touched the screen. This embodiment offers a moreefficient approach to generating pixel coordinate estimates thatminimizes delays, reduces corruption of estimates due to noise, enhancesESD protection, and eliminates the need for user-interactivecalibration. The pixel coordinate estimates are characterized as digitalsignal values in a processor of the touch-screen display system. Thesedigital signal values are generated, in part, from a set of analogvoltage levels, sampled from analog resistive screens in thetouch-screen display system, corresponding to the position of where auser has touched the display screen.

[0033]FIG. 1 is a schematic block diagram of certain elements of thetouch-screen display system 10 made in accordance with one embodiment ofthe invention. These elements comprise analog resistive screens 20 and30 that include conductive bus bars 40, 50, 60, and 70, and resistivematerials 80 and 90. An active area 25 of the screens 20, 30 is definedby the overlap of the screens 20, 30 as the display screen, and anactive area of the display is shown by reference numeral 35. Additionalelements comprise drivers 100, 110, 120, and 130, analog-to-digitalconverters 140, 150, 160, and 170, and shunts 180 and 190 and capacitors195. The capacitors 195 may be inherent or added physical elements.

[0034] Referring to FIG. 1, the resistive material 90 of the analogresistive screen 30 is electrically connected between a top bus bar 40and a bottom bus bar 50. The resistive material 80 of the analogresistive screen 20 is electrically connected between a left bus bar 60and a right bus bar 70. Each bus bar is electrically connected to anassociated driver 100, 110, 120, 130 and an analog-to-digital converter140, 150, 160, 170 as shown in FIG. 1. In this embodiment of theinvention, the drivers 100, 110, 120, 130 are bi-polar transistors eachcomprising a base terminal 200, an emitter terminal 210, and a collectorterminal 220. The drivers are electrically connected to the associatedbus bars at the collector terminals 220 and provide reference signalsthrough reference signal interfaces 230, 240, 250, and 260 to the busbars when the drivers are turned on. The analog-to-digital convertersare electrically connected to the bus bars through analog interfaces270, 280, 290, and 300.

[0035]FIG. 2 is a schematic block diagram of the processor 310 of thetouch-screen display system with its associated software algorithmscomprising a validity algorithm 320, a calibration algorithm 330, and acorrection algorithm 340. This processor 310 interfaces to the elementsin FIG. 1.

[0036] The base terminals 200 of the drivers 100, 110, 120, and 130interface to the processor 310 through driver signal interfaces 350,360, 370, and 380 as shown in FIGS. 1 and 2. The analog-to-digitalconverters 140, 150, 160, and 170 interface to the processor 310 throughdigital signal interfaces 390, 400, 410, and 420.

[0037] The shunt 180 electrically connects across the driver 100 at itsemitter terminal 210 and collector terminal 220. The shunt 190electrically connects across the driver 110 at its emitter terminal 210and collector terminal 220. In this embodiment of the invention, theshunts 180 and 190 are a resistor and capacitor 195 in parallel butcould be resistors or some other combination of components to establishpre-determined discharge rates which determine settling times on theanalog interfaces. Alternatively, these components may not be needed ifeither low side or the high drivers 100, 110, 120, 130 are selected tohave an appropriate off state impedance to establish pre-determineddischarge or charge rates or if the low side or high drivers 100, 110,120 130 are controlled to establish predetermined discharge or chargerates. Also, the shunts 180, 190 could be placed in parallel to the highside drivers 120, 130 or the low side drivers 100, 110.

[0038] The eight signal interfaces 230-300 form an 8-wire configurationthat allows for alternate sampling of analog voltage signals andreference signals with only one analog-to-digital converter/driver pairfor each bus bar.

[0039] In a touch-screen display system of one embodiment of theinvention, a user presses at a particular location (usually representedas a key) on a display screen. The system samples an x-axis 430 and thena y-axis 440 of the display screen to determine the pixel coordinatelocations of where the screen is touched. In the present invention, thex sample is validated before the y sample is examined.

[0040] Referring to FIGS. 1 and 2, the processor 310 drives a first axisof the touch-screen display system 10 such as the horizontal or x-axis430 by turning on the drivers 110 and 130. At this time the drivers 100and 120, corresponding to the vertical or y-axis 440, are turned off bythe processor 310. When the driver 110 is turned on, it establishes alow impedance reference path through the reference signal interface 240from the right bus bar 70 to a ground reference 450. When the driver 130is turned on, it provides a voltage reference through the voltagereference interface 460 to the left bus bar 60 through the referencesignal interface 260.

[0041] The voltage reference applied to the left bus bar 60 and theground reference applied to the right bus bar 70 in conjunction with theresistive material 80 creates a varying voltage potential with respectto the ground reference 450 across the analog resistive screen 20 atdifferent points along the x-axis 430. When a user touches the displayscreen, the analog resistive screen 30 makes electrical contact with theanalog resistive screen 20 at a defined point having a particular x-ypixel location. The analog resistive screen 30 is then at the voltagepotential corresponding to that point along the x-axis 430 on the analogresistive screen 20. The bus bars 40 and 50 are, therefore, also at thissame potential with respect to the ground reference 450, creating ananalog voltage signal on analog interfaces 270 and 290.

[0042] Since the driver 120 is turned off, this allows for a correctmeasurement of the analog voltage signal on the upper bus bar 40 at theanalog interface 290 by the analog-to-digital converter 160.

[0043] Alternatively, since the driver 100 is turned off, it allows ahigh impedance path to exist between the lower bus bar 50 and the groundreference 450 through the shunt 180. The shunt 180 has a high impedancevalue compared to the impedance of the analog resistive screen 20. Thisallows for a correct measurement of the analog voltage signal on theanalog interface 270 by the analog-to-digital converter 140.

[0044] The analog voltage signal on the analog interface 290 isconverted to a digital signal, known as X_(raw), on the digital signalinterface 410 and represents a pixel location along the x-axis 430corresponding to where the user is touching the display screen. Thisdigital signal X_(raw) is read by a processor 310. The left bus barvoltage reference level, known as X_(max), on the analog interface 300and the right bus bar voltage reference level, known as X_(min), on theanalog interface 280 are also digitized and read by the processor 310 ina similar manner. The 8-wire configuration allows for the sampling ofthese signals and reference levels with only one analog-to-digitalconverter/driver pair for each bus bar.

[0045] Once the x-axis pixel position samples (X_(raw), X_(max),X_(min)) have been read and validated, the process is preferablyrepeated for the y-axis 440 in a similar manner where, now, the drivers130 and 110 are turned off and the drivers 100 and 120 are turned on. Avarying voltage potential is created across the analog resistive screen30 and the analog resistive screen 20 is at the voltage potentialcorresponding to the pixel location along the y-axis 440 where the twoscreens are touching. In this way, the digital signal, known as Y_(raw),on the digital interface 420 is generated and represents a pixellocation along the y-axis 440 corresponding to where the user istouching the display screen. This digital signal Y_(raw) is read by theprocessor 310. The upper bus bar voltage reference level, known asY_(max), on the analog interface 290 and the lower bus bar voltagereference level, known as Y_(min), on the analog interface 270 are alsodigitized and read by the processor 310 in a similar manner.

[0046] Touch-screen display systems often need to be calibrated, forexample, to eliminate errors in the pixel coordinate estimatesintroduced by drifting voltage references and ground references, or bychanges in the resistive characteristics of the analog resistivematerial. Factors such as temperature, humidity, and aging can causethese undesirable effects. Another feature of the disclosed embodimentis the technique that is used for calibration. The previously describedtechnique of sampling the signals and references (X_(raw), X_(max),X_(min), Y_(raw), Y_(max), Y_(min)) allows for the calibration techniqueto be implemented since, by measuring the actual voltage levels on theanalog resistive screens, any errors can be calibrated out as describedbelow.

[0047]FIG. 3 is a flowchart showing the steps of the calibrationalgorithm 330 that is called by the validity algorithm 320 as part ofits operation. In step 470 of the calibration algorithm 330, theprocessor 310 samples the signals and references for a particular drivenaxis such as signals and references X_(raw), X_(max), X_(min) or signalsand references Y_(raw), Y_(max), Y_(min) represented more generally inthe flowchart as V_(raw), V_(max), V_(min). In step 480, the processor310 calculates a numerator parameter as (V_(raw)−V_(min)) representingthe voltage level at the pixel coordinate position on the analogresistive screen with respect to the ground reference. In step 490, theprocessor 310 calculates a denominator parameter as (V_(max)−V_(min))representing the actual voltage potential (or range) applied across theanalog resistive screen. In step 500, the processor 310 calculates aratio parameter as the numerator parameter divided by the denominatorparameter or (V_(raw)−V_(min))/(V_(max)−V_(min)). This ratio parameterrepresents the percentage of how far along the axis the screen wastouched by the user. As a final step 510, the processor 310 multipliesthe ratio parameter by the known number of pixels N_(pix) across theaxis of the screen. This yields a calibrated pixel coordinate estimatein units of pixels for the axis. This process can be done in real-timeduring normal operation of the touch-screen display system and does notrequire the user to touch the display screen at any pre-definedlocations. There is no calibration process that needs to be doneseparate from normal operation. The calibration process is transparentto the user. This calibration process is accomplished for each axis ofthe touch-screen display system.

[0048] Even though the pixel coordinate estimates have errors, forexample, due to drift calibrated out by the calibration algorithm 330,there can still be errors due to noise. One way to minimize noise due tosuch things as settling times of the drivers is to insert significantdelay times into the sampling process to allow the drivers and varioussignals to settle out. This is inefficient and wastes time and does notnecessarily eliminate noise from other sources.

[0049]FIG. 4 is a flowchart of a validity algorithm 320 that is used tocontrol how pixel coordinate estimates are sampled and validated asbeing good estimates. This algorithm has the effect of minimizingsampling delay times and eliminating noisy estimates that cause errorsin determining the pixel position. In steps 520, 530, and 540 of thevalidity algorithm 320, the processor 310 drives the x-axis 430 aspreviously described by turning on the drivers 110 and 130 to determinea value for N_(pos). In determining X_(pos), a first calibrated pixelcoordinate estimate X_(raw1) and a second calibrated pixel coordinateestimate X_(raw2) are generated, preferably consecutively, by theprocessor 310 using the calibration algorithm 330. Although thepreferred embodiment is described in terms of two samples or estimates,a person of ordinary skill in the art will recognize that three or moresamples may be also used, and either averaged, prorated, or combined orselected in any conventional manner. These estimates are separated intime by a pre-determined sampling interval. In step 550, the processorgenerates a first comparison parameter value as |X_(raw1)−X_(raw2)| andcompares this first comparison parameter value to a pre-determined firstthreshold value N₁. If the first comparison parameter value is greaterthan N₁, then the estimates are defined to be invalid and the processor310 makes another attempt to generate a valid estimate. If the firstcomparison parameter value is less than N₁, then the processorpreferably takes X_(raw2) as the valid pixel coordinate estimate, nowX_(pos), for the x-axis and proceeds to generate y-axis estimates.Alternately, X_(raw1) may be selected as the valid pixel coordinates, orX_(raw1) and X_(raw2) may be combined either pro rata or using any otherformula or function. The processor makes, at most, a predeterminednumber of attempts to generate a valid estimate for the x-axis. Thispre-determined number of attempts is typically two in the disclosedembodiment but may be varied to three or more. If, after thispre-determined number of attempts, a valid x-axis estimate is notdetermined, then the processor defines a “no touch” state and generatesa “no touch” parameter value to indicate the “no touch” state. This “notouch” state is interpreted as the display screen not being touched by auser.

[0050] The pre-determined sampling interval, the shunt 180, and thepredetermined difference N₁ are all chosen such that the resultantsettling time (corresponding to a discharge rate of the capacitors 195associated with the corresponding analog interfaces and drivers) allowsa distinguishing voltage difference between two successive samples atthe analog interface 290, and therefore at the input to theanalog-to-digital converter 160, when the display screen is not beingtouched. This voltage difference between samples when the display screen25 is not being touched is different than the voltage difference betweensamples when the display screen 25 is being touched because the settlingtime (discharge rate) is changed when the display has been touched. Thisis because, when the display screen 25 is being touched, the sensingscreen is actively being charged and the settling time is based muchmore on the low impedance of the drivers than the higher impedance ofthe shunt. Therefore, the shunt 180 or 190, in conjunction with thesampling interval, N₁, and validity algorithm allows determination of avalid estimate of a “no touch” state. By generating at least twoestimates, the sampling time interval between the estimates can bepre-defined such that the need for significant delay times is eliminatedwhen generating the estimates. This also allows inexpensive capacitance195 to be added to the analog interfaces and drivers for enhanced ESDprotection, increasing the settling times without increasing the delaybefore sampling. This added capacitance increases the settling times ofthe analog interfaces but the method of sampling and validating thesamples eliminates the need to wait until after these settling timesbefore sampling. In this way, more expensive components for ESDprotection such as zener diodes can be avoided.

[0051] Once a valid x-axis pixel coordinate estimate has beendetermined, the processor 310 then attempts to generate a valid y-axispixel coordinate estimate in a similar manner to determine a value forY_(pos). Steps 560-600 in the validity algorithm 320 illustrate thisprocess. A first estimate Y_(raw1) is generated along with a secondestimate Y_(raw2). Although the preferred embodiment is described interms of two samples or estimates, a person of ordinary skill in the artwill recognize that three or more samples may be also used, and eitheraveraged, prorated, or combined or selected in any conventional manner.A second comparison parameter value is calculated and compared to asecond threshold value N₂. This threshold value N₂ may be the same asthreshold value N₁ or not, depending on the exact implementation.Y_(raw2) is preferably taken as the valid y-axis estimate, now Y_(pos),if the second comparison value is less than N₂, otherwise the processorattempts to generate valid pixel coordinate value estimates by startingover at step 520 to again determine a valid x-axis estimate beforedetermining a valid y-axis estimate. Again, after a pre-determinednumber of attempts, a “no touch” state is defined and a “no touch”parameter value is generated. Similarly, the pre-determined samplinginterval, the shunt 190, and the predetermined difference N₂ are allchosen such that the resultant settling time (corresponding to adischarge rate of the capacitance associated with the correspondinganalog interfaces) allows a distinguishing voltage difference betweentwo successive samples at the analog interface 300, and therefore at theinput to the analog-to-digital converter 170, when the display screen isnot being touched. Again, this allows inexpensive capacitance 195 to beadded to the analog interfaces and drivers for enhanced ESD protection,increasing the settling times without increasing the wait beforesampling.

[0052] If the active areas 25, 35 of the display of the touch-screendisplay system and analog resistive screens line up and are equivalentby design and the bus bars are at the edges of the active areas of thescreens, then the previously calculated calibrated pixel coordinateestimates do not need any further correction. In many touch-screendisplay systems, however, the bus bars are not at the edge of the activeareas of the screens; there is some lead-in distance between the bus barand the active areas of the screens. Additionally, if there is an offset98, 99 between the edges of the active areas of the screens and thedisplay of the touch-screen display system, then further corrections tothe calibrated pixel coordinate estimates are made. Generally, theseoffsets 98, 99 are known or determined at time of manufacture butalternatively the offsets could be determined and entered at a laterdate.

[0053] In this embodiment of the invention, these corrections are madeby the correction algorithm 340 to the calibrated pixel coordinateestimates as described below.

[0054] The correction factors for the distance between the bus bars andthe active area for the x-axis are

[0055] X_(Lcorrection)=(the greater of the distance between the left busbar and the analog resistive screen active area or the distance betweenthe left bus bar and the display active area)/distance between the leftand right bus bars, and

[0056] X_(Rcorrection)=(the greater of distance between right bus barand analog resistive screen active area or distance between right busbar and display active area)/distance between the left and right busbars.

[0057] These two correction factors can be normalized toanalog-to-digital converter bits by multiplying them by X_(range) whichequals (X_(max)−X_(min)), yielding the equation

X position (pixels)=pixels_(—) ux*(X _(pos) −X _(min)−(X _(range) *X_(Lcorrection)))/(X _(range)*(1−X _(Lcorrection) −X _(Rcorrection))

[0058] where pixels_ux is the number of display pixels under the activearea of the analog resistive screen along the x-axis. For the y-axis thecorrection factors are

[0059] Y_(Tcorrection)=(the greater of the distance between the top busbar and the analog resistive screen active area or the distance betweenthe top bus bar and the display active area)/the distance between thetop and bottom bus bars, and

[0060] Y_(Bcorrection)=(the greater of the distance between the bottombus bar and the analog resistive screen active area or the distancebetween the bottom bus bar and the display active area)/the distancebetween the top and bottom bus bars.

[0061] These two correction factors can be normalized toanalog-to-digital converter bits by multiplying them by Y_(range) whichequals (Y_(max)−Y_(min)), yielding the equation

Y position (pixels)=pixels_(—) uy*(Y _(pos) −Y _(min)−(Y _(range) *Y_(Bcorrection)))/(Y _(range)*(1−Y _(correction) −B _(correction))

[0062] where pixels_uy is the number of display pixels under the activearea of the analog resistive screen along the y-axis.

[0063] These equations yield corrected, calibrated pixel coordinateestimates.

[0064] If it is desired to have the (0,0) position be defined in theupper left instead of the lower left, simply subtract the normalizedposition from one before multiplying by pixels in software as

Y position (pixels)=pixels_(—) uy*[1−(Y _(pos) −Y _(min)−(Y _(range) *Y_(Bcorrection)))/(Y _(range)*(1−Y _(Tcorrection) −Y _(Bcorrection))]

[0065] The (0,0) position also can be defined in the upper left insteadof the lower left by reversing the low and high side drivers for they-axis so that the higher voltage is applied to the bottom bus bar.

[0066] A ratiometric analog-to-digital converter may be used instead ofthe four analog-to-digital converters and still get the benefits of thecorrections by replacing X_(min) and Y_(min) with zero; and replacingX_(range) and Y_(range) with the maximum count output of theanalog-to-digital converter.

[0067] While the invention is described in connection with oneembodiment, it will be understood that the invention is not limited tothat one embodiment. On the contrary, the invention covers allalternatives, modifications, and equivalents within the spirit and scopeof the appended claims.

[0068] For example, some possible alternatives might include thefollowing described below. The shunts may be a resistor (possibly forESD protection) or some other combination of components to establishpre-defined settling times (discharge rates). The drivers may be someother form of switching circuit besides a bipolar transistor. In thevalidity algorithm, the y-axis could be driven and sampled before thex-axis. The processor does not have to be one entity. It could comprisemultiple hardware units.

[0069] Other variations may include the following described below. Thevalidity algorithm, calibration algorithm, and correction algorithm canbe integrated with each other to a lesser extent or a greater extent.For example, the three algorithms could essentially be one largealgorithm, or they could be three relatively independent algorithms thatoperate in conjunction with each other.

[0070] The validity algorithm may use some other number of multiplesamples per axis besides just two samples for determination of a validpixel coordinate estimate. The validity algorithm may also employ someother form of comparison parameter such as a ratio of the samplesinstead of a difference, along with an appropriate, correspondingthreshold. Similarly, the correction and calibration algorithm may takemore than two samples, then use a selected one or more of those samplesto determine a coordinate.

[0071] “No touch” detection could be done independent of the validityalgorithm by just comparing the value of a single pixel coordinatesample to a threshold for determination of a “no touch” state. This mayinclude, for example, that the voltage level sampled across the shunt,when the driver is turned off and the screen is not being touched, isalways lower than the voltage level sampled when the driver is turnedoff and the screen is being touched. In other words, the minimum voltagelevel sampled corresponding to the minimum pixel location of an axis isgreater than the “no touch” voltage level.

[0072] In summary, the advantages and features found in at least oneembodiment of the invention include among others:

[0073] No external procedure or touching of specific areas of thedisplay screen is required to obtain or maintain calibration.Calibration is automatic, continuous and does not interfere with use ofthe touch-screen display system. A pixel position is generated that isaccurate to sub-pixel precision through the life of the touch-screendisplay system despite temperature variation, humidity variation, agingof components, and initial component variation.

[0074] The display active area need not be matched to the active areasof the analog resistive screens. Delays in sampling due to settlingtimes are minimized and effects of noise are minimized. Minimal softwarefiltering of samples is required for accurate and noise free operation.Inexpensive capacitors can be added to the analog interfaces and driversfor ESD protection instead of using, for example, zener diodes (savingten cents to a dollar per touch screen). This added capacitanceincreases the settling times of the analog interfaces but the method ofsampling and validating the samples eliminates the need to wait untilafter these settling times before sampling. Lower cost components can beused. For example, a more expensive analog-to-digital converter withratiometric inputs is not required. The drivers need not be low voltagedrop and the driver gain need not be high. The tolerances of theresistance in the wiring, analog resistive screen active areas, andtraces need not be tight.

What is claimed is:
 1. In a touch-screen display system for generatingpixel coordinate estimates responsive to a user touching a displayscreen, an apparatus for calibrating said touch-screen display systemcomprising: a processor responsive to digital signals from saidtouch-screen display system to generate calibrated pixel coordinateestimates as an integral part of real-time generation of said pixelcoordinate estimates without needing said user to assist in thecalibration effort by touching pre-determined locations on said displayscreen.
 2. The apparatus of claim 1 wherein said digital signals arederived from voltage levels sampled from bus bars of analog resistivescreens within said touch-screen display system.
 3. The apparatus ofclaim 2 wherein said voltage levels are converted to said digitalsignals by a set of analog-to-digital converters within saidtouch-screen display system.
 4. The apparatus of claim 2 wherein saidanalog resistive screens are powered on and powered off by drivers thatapply voltage reference levels to said bus bars of said analog resistivescreens.
 5. The apparatus of claim 4 wherein said drivers are controlledby said processor.
 6. The apparatus of claim 2 wherein said touch-screendisplay system is configured to sample at least eight independentdigital signals corresponding to at least eight independent voltagelevels on said bus bars of said analog resistive screens andcorresponding to various combinations of said analog resistive screensbeing powered on, powered off, touched, and not touched.
 7. Theapparatus of claim 1 wherein said digital signals comprise a firstdigital signal and a second digital signal and a third digital signal.8. The apparatus of claim 7 wherein said first digital signalcorresponds to a voltage level sampled from a bus bar of a second analogresistive screen of said touch-screen display system that is not poweredon and is touching a first analog resistive screen of said touch-screendisplay system that is powered on.
 9. The apparatus of claim 8 whereinsaid second digital signal corresponds to a ground reference sampledfrom a first bus bar of said first analog resistive screen.
 10. Theapparatus of claim 9 wherein said third digital signal corresponds to avoltage reference level sampled from a second bus bar of said firstanalog resistive screen.
 11. The apparatus of claim 10 wherein saidprocessor is programmed to generate a numerator parameter valuerepresenting the difference between said first digital signal and saidsecond digital signal.
 12. The apparatus of claim 11 wherein saidprocessor is responsive to said third digital signal and said seconddigital signal to generate a denominator parameter value representingthe difference between said third digital signal and said second digitalsignal.
 13. The apparatus of claim 12 wherein said processor isresponsive to said numerator parameter value and said denominatorparameter value to generate a ratio parameter value representing theratio of said numerator parameter value and said denominator parametervalue.
 14. The apparatus of claim 13 wherein said processor isresponsive to said ratio parameter value and a number of pixels thatfully spans a corresponding axis of said touch-screen display system togenerate a calibrated pixel coordinate estimate representing the productof said ratio parameter value and said number of pixels.
 15. Theapparatus of claim 2 wherein said processor is responsive to saidcalibrated pixel coordinate estimates to generate corrected calibratedpixel coordinate estimates due to any mismatch between spatial locationsof said bus bars of said analog resistive screens and edges of activeareas of said analog resistive screens.
 16. The apparatus of claim 2wherein said processor is responsive to said calibrated pixel coordinateestimates to generate corrected calibrated pixel coordinate estimatesdue to any mismatch between spatial locations of edges of active areasof said analog resistive screens and active areas of a display of saidtouch-screen display system.
 17. In a touch-screen display system forgenerating pixel coordinate estimates responsive to a user touching adisplay screen, an apparatus for generating and validating said pixelcoordinate estimates comprising: a processor to determine a first validpixel coordinate estimate for a first touch-screen axis of saidtouch-screen display system before determining a second valid pixelcoordinate estimate for a second touch-screen axis of said touch-screendisplay system.
 18. The apparatus of claim 17 wherein said processor isadapted to power on said first touch-screen axis of said touch-screendisplay system and to power off said second touch-screen axis of saidtouch-screen display system.
 19. The apparatus of claim 18 wherein saidfirst touch-screen axis is an x-axis and said second touch-screen axisis a y-axis.
 20. The apparatus of claim 18 wherein said processor isadapted to generate a first pixel coordinate estimate corresponding tosaid first touch-screen axis and a second pixel coordinate estimatecorresponding to said first touch-screen axis such that said first pixelcoordinate estimate and said second pixel coordinate estimate areseparated in time by a pre-determined sampling interval.
 21. Theapparatus of claim 20 wherein said processor is responsive to said firstpixel coordinate estimate of said first touch-screen axis and saidsecond pixel coordinate estimate of said first touch-screen axis togenerate a first comparison parameter value.
 22. The apparatus of claim21 wherein said processor is adapted to read a pre-determined firstthreshold value.
 23. The apparatus of claim 22 wherein said processor isadapted to compare said first comparison parameter value to saidpre-determined first threshold value.
 24. The apparatus of claim 23wherein said processor is adapted to select said second pixel coordinateestimate of said first touch-screen axis as a first valid pixelcoordinate estimate of said first touch-screen axis if said firstcomparison parameter value is in a first definite relationship to saidpre-determined first threshold value.
 25. The apparatus of claim 23wherein said processor is adapted to define said first valid pixelcoordinate estimate as invalid if said first comparison parameter valueis in a second definite relationship to said pre-determined firstthreshold value.
 26. The apparatus of claim 25 wherein said processor isadapted to make, at most, a pre-determined number of attempts togenerate and select said first valid pixel coordinate estimate.
 27. Theapparatus of claim 25 wherein said processor is adapted to define a “notouch” state as being detected and to generate a “no touch” parametervalue to indicate said “no touch” state as being detected when saidfirst valid pixel coordinate estimate is defined as invalid.
 28. Theapparatus of claim 26 wherein said processor is adapted to define said“no touch” state as being detected by generating a “no touch” parametervalue to indicate said “no touch” state as being detected if saidpre-determined number of attempts is reached and said processor stilldefines said first valid pixel coordinate estimate as invalid.
 29. Theapparatus of claim 17 wherein said processor is adapted to power on saidsecond touch-screen axis of said touch-screen display system and topower off said first touch-screen axis of said touch-screen displaysystem.
 30. The apparatus of claim 29 wherein said processor is adaptedto generate a first pixel coordinate estimate corresponding to saidsecond touch-screen axis and a second pixel coordinate estimatecorresponding to said second touch-screen axis such that said firstpixel coordinate estimate and said second pixel coordinate estimate areseparated in time by a pre-determined sampling interval.
 31. Theapparatus of claim 30 wherein said processor is responsive to said firstpixel coordinate estimate of said second touch-screen axis and saidsecond pixel coordinate estimate of said second touch-screen axis togenerate a second comparison parameter value.
 32. The apparatus of claim31 wherein said processor is adapted to read a pre-determined secondthreshold value.
 33. The apparatus of claim 32 wherein said processor isadapted to compare said second comparison parameter value to saidpre-determined second threshold value.
 34. The apparatus of claim 33wherein said processor is adapted to select said second pixel coordinateestimate of said second touch-screen axis as a second valid pixelcoordinate estimate of said second touch-screen axis if said secondcomparison parameter value is in a first definite relationship to saidpredetermined second threshold value.
 35. The apparatus of claim 33wherein said processor is adapted to define said second valid pixelcoordinate estimate as invalid if said second comparison parameter valueis in a second definite relationship to said predetermined secondthreshold value.
 36. The apparatus of claim 35 wherein said processor isadapted to generate and select said first valid pixel coordinateestimate corresponding to said first touch-screen axis before makinganother attempt to generate and select said second valid pixelcoordinate estimate corresponding to said second touch-screen axis. 37.The apparatus of claim 36 wherein said processor is adapted to make, atmost, a pre-determined number of attempts to generate and select saidsecond valid pixel coordinate estimate.
 38. The apparatus of claim 35wherein said processor is adapted to define a “no touch” state as beingdetected and to generate a “no touch” parameter value to indicate said“no touch” state as being detected when said second valid pixelcoordinate estimate is defined as invalid.
 39. The apparatus of claim 37wherein said processor is adapted to define said “no touch” state asbeing detected by generating a “no touch” parameter value to indicatesaid “no touch” state as being detected if said pre-determined number ofattempts is reached and said processor still defines said second validpixel coordinate estimate as invalid.
 40. In a touch-screen displaysystem for generating pixel coordinate estimates responsive to a usertouching a display screen, an apparatus for enabling detection of a “notouch” state of said touch-screen display system comprising: at leastone bus bar; at least one driver electrically connected to said at leastone bus bar to selectively switch said at least one bus bar between atleast two of a plurality of electrical potentials; and at least oneshunt electrically connected across said at least one driver.
 41. Theapparatus of claim 40 wherein said plurality of electrical potentialscomprises a plurality of voltage levels with respect to an electricalground representative of said pixel coordinate estimates.
 42. Theapparatus of claim 41 wherein said at least one driver comprises atransistor.
 43. The apparatus of claim 42 wherein said transistorcomprises an emitter terminal and a collector terminal.
 44. Theapparatus of claim 43 wherein said at least one shunt is electricallyconnected across said collector terminal and said emitter terminal ofsaid transistor.
 45. The apparatus of claim 43 wherein said collectorterminal is electrically connected to said at least one bus bar and saidemitter terminal is electrically connected to said electrical ground.46. The apparatus of claim 40 wherein said at least one shunt comprisesa resistor.
 47. The apparatus of claim 41 wherein said at least oneshunt provides an impedance path from said at least one bus bar to saidelectrical ground.
 48. The apparatus of claim 40 wherein said at leastone shunt determines, at least in part, a settling time (discharge rate)corresponding to at least one analog interface of said touch-screendisplay system.
 49. The apparatus of claim 41 wherein said at least onebus bar is electrically connected to said electrical ground through saidat least one driver when said at least one driver is powered on.
 50. Theapparatus of claim 41 wherein said at least one bus bar is at one ofsaid plurality of voltage levels when said at least one driver ispowered off and said display screen is being touched by a user.
 51. Theapparatus of claim 41 wherein said at least one bus bar is electricallyconnected to said electrical ground through said shunt when said atleast one driver is powered off and said display screen is not beingtouched by a user.
 52. The apparatus of claim 41 further comprising atleast one analog-to-digital converter electrically connected to said atleast one bus bar to convert said plurality of voltage levels to aplurality of digital values representing said plurality of voltagelevels.
 53. The apparatus of claim 52 further comprising a processorresponsive to said plurality of digital values for subsequent detectionof said “no touch” state.
 54. The apparatus of claim 48 wherein athreshold value is determined, at least in part, by said settling time(discharge rate) and said sampling rate, and is used in determining thevalidity of said pixel coordinate estimates.
 55. In a touch-screendisplay system for generating pixel coordinate estimates responsive to auser touching a display screen, a method for calibrating axes of saidtouch-screen display system comprising: generating calibrated pixelcoordinate estimates in response to digital signals from saidtouch-screen display system as an integral part of real-time generationof said pixel coordinate estimates without needing said user to assistin the calibration effort by touching pre-determined locations on saiddisplay screen.
 56. The method of claim 55 further comprising generatingsaid digital signals from voltage levels sampled from reference pointsof said axes within said touch-screen display system.
 57. The method ofclaim 56 further comprising converting said voltage levels to saiddigital signals within said touch-screen display system.
 58. The methodof claim 56 further comprising powering on and powering off saidreference points using driving techniques to apply voltage referencelevels to said reference points.
 59. The method of claim 56 furthercomprising sampling at least eight independent digital signalscorresponding to at least eight independent voltage levels on saidreference points and corresponding to various combinations of saidreference points of said axes being powered on and powered off, and saidtouch-screen display system being touched and not touched.
 60. Themethod of claim 55 wherein said digital signals comprise a first digitalsignal and a second digital signal and a third digital signal.
 61. Themethod of claim 60 wherein said first digital signal corresponds to avoltage level sampled from a second reference point of a second axis ofsaid touch-screen display system that is not powered on but iselectrically touching a first axis of said touch-screen display systemthat is powered on.
 62. The method of claim 61 wherein said seconddigital signal corresponds to a ground reference sampled from a firstreference point of said first axis.
 63. The method of claim 62 whereinsaid third digital signal corresponds to a voltage reference levelsampled from a second reference point of said first axis.
 64. The methodof claim 63 further comprising generating a numerator parameter valuerepresenting the difference between said first digital signal and saidsecond digital signal.
 65. The method of claim 64 further comprisinggenerating a denominator parameter value representing the differencebetween said third digital signal and said second digital signal. 66.The method of claim 65 further comprising generating a ratio parametervalue representing the ratio of said numerator parameter value and saiddenominator parameter value.
 67. The method of claim 66 furthercomprising generating a calibrated pixel coordinate estimaterepresenting the product of said ratio parameter value and a number ofpixels that fully spans a corresponding axis of said touch-screendisplay system.
 68. The method of claim 56 further generating correctedcalibrated pixel coordinate estimates from said calibrated pixelcoordinate estimates correcting for any mismatch between spatiallocations of said reference points and edges of active areas of saidtouch-screen display system.
 69. The method of claim 56 furthercomprising generating corrected calibrated pixel coordinate estimatesfrom said calibrated pixel coordinate estimates correcting for anymismatch between various spatial locations of edges of active areas ofsaid touch-screen display system.
 70. In a touch-screen display systemfor generating pixel coordinate estimates responsive to a user touchinga display screen, a method for generating and validating said pixelcoordinate estimates comprising: generating and determining the validityof a first valid pixel coordinate estimate for a first touch-screen axisof said touch-screen display system before generating and determiningthe validity of a second valid pixel coordinate estimate for a secondtouch-screen axis of said touch-screen display system.
 71. The method ofclaim 70 further comprising powering on said first touch-screen axis ofsaid touch-screen display system and powering off said secondtouch-screen axis of said touch-screen display system.
 72. The method ofclaim 71 wherein said first touch-screen axis is an x-axis and saidsecond touch-screen axis is a y-axis.
 73. The method of claim 71 furthercomprising generating a first pixel coordinate estimate corresponding tosaid first touch-screen axis and a second pixel coordinate estimatecorresponding to said first touch-screen axis such that said first pixelcoordinate estimate and said second pixel coordinate estimate areseparated in time by a pre-determined sampling interval.
 74. The methodof claim 73 further comprising generating a first comparison parametervalue from said first pixel coordinate estimate of said firsttouch-screen axis and said second pixel coordinate estimate of saidfirst touch-screen axis.
 75. The method of claim 74 further comprisingcomparing said first comparison parameter value to a predetermined firstthreshold value.
 76. The method of claim 75 further comprising selectingsaid second pixel coordinate estimate of said first touch-screen axis asa first valid pixel coordinate estimate of said first touch-screen axisif said first comparison parameter value is in a first definiterelationship to said pre-determined first threshold value.
 77. Themethod of claim 75 further comprising defining said first valid pixelcoordinate estimate as invalid if said first comparison parameter valueis in a second definite relationship to said pre-determined firstthreshold value.
 78. The method of claim 77 further comprising making,at most, a pre-determined number of attempts to generate and select saidfirst valid pixel coordinate estimate.
 79. The method of claim 77further comprising defining a “no touch” state as being detected andgenerating a “no touch” parameter value to indicate said “no touch”state as being detected when said first valid pixel coordinate estimateis defined as invalid.
 80. The method of claim 78 further comprising a“no touch” state as being detected by generating a “no touch” parametervalue to indicate said “no touch” state as being detected if saidpre-determined number of attempts is reached and said first valid pixelcoordinate estimate is still defined as invalid.
 81. The apparatus ofclaim 70 further powering on said second touch-screen axis of saidtouch-screen display system and powering off said first touch-screenaxis of said touch-screen display system.
 82. The method of claim 81further generating a first pixel coordinate estimate corresponding tosaid second touch-screen axis and a second pixel coordinate estimatecorresponding to said second touch-screen axis such that said firstpixel coordinate estimate and said second pixel coordinate estimate areseparated in time by a pre-determined sampling interval.
 83. The methodof claim 82 further comprising generating a second comparison parametervalue from said first pixel coordinate estimate of said secondtouch-screen axis and said second pixel coordinate estimate of saidsecond touch-screen axis.
 84. The method of claim 83 further comprisingcomparing said second comparison parameter value to a pre-determinedsecond threshold value.
 85. The method of claim 84 further comprisingselecting said second pixel coordinate estimate of said secondtouch-screen axis as a second valid pixel coordinate estimate of saidsecond touch-screen axis if said second comparison parameter value is ina first definite relationship to said pre-determined second thresholdvalue.
 86. The method of claim 84 further comprising defining saidsecond valid pixel coordinate estimate as invalid if said secondcomparison parameter value is in a second definite relationship to saidpre-determined second threshold value.
 87. The method of claim 86further comprising generating and selecting said first valid pixelcoordinate estimate corresponding to said first touch-screen axis beforeagain attempting to generate and select said second valid pixelcoordinate estimate corresponding to said second touch-screen axis. 88.The method of claim 87 further comprising making, at most, apredetermined number of attempts to generate and select said secondvalid pixel coordinate estimate.
 89. The method of claim 86 furthercomprising defining a “no touch” state as being detected and generatinga “no touch” parameter value to indicate said “no touch” state as beingdetected when said second valid pixel coordinate estimate is defined asinvalid.
 90. The method of claim 88 further comprising said “no touch”state as being detected by generating a “no touch” parameter value toindicate said “no touch” state as being detected if said pre-determinednumber of attempts is reached and said second valid pixel coordinateestimate is still defined as invalid.
 91. In a touch-screen displaysystem for generating pixel coordinate estimates responsive to a usertouching a display screen, a method for enabling detection of a “notouch” state of said touch-screen display system comprising: selectivelyswitching at least one reference point of at least one axis of saidtouch-screen display system between at least two of a plurality ofelectrical potentials by employing electrical driving techniques andelectrical shunting techniques.
 92. The method of claim 91 wherein saidplurality of electrical potentials comprises a plurality of voltagelevels with respect to an electrical ground representative of said pixelcoordinate estimates.
 93. The method of claim 91 wherein at least two ofsaid plurality of electrical potentials comprise a voltage referencelevel and an electrical ground.
 94. The method of claim 92 furthercomprising providing an impedance path from said at least one referencepoint of said at least one axis to said electrical ground using saidelectrical shunting techniques.
 95. The method of claim 91 furthercomprising establishing a settling time (discharge rate) of said atleast one reference point using said electrical shunting techniques. 96.The method of claim 92 further comprising electrically connecting saidat least one reference point of said at least one axis to saidelectrical ground when said at least one axis is powered on, using saidelectrical driving techniques.
 97. The method of claim 92 wherein saidat least one reference point of said at least one axis is at one of saidplurality of voltage levels when said at least one axis is powered offand said user is touching said 15 touch-screen display system.
 98. Themethod of claim 94 further comprising electrically connecting said atleast one reference point of said at least one axis to said electricalground through said impedance path when said at least one axis ispowered off and said user is not touching said touch-screen displaysystem, using said electrical driving techniques.
 99. The method ofclaim 92 further comprising converting said plurality of voltage levelsto a plurality of digital signals representing said plurality of voltagelevels.
 100. The method of claim 99 further comprising processing saidplurality of digital signals for subsequent detection of said “no touch”state.
 101. The method of claim 95 further comprising pre-determining athreshold value from, at least in part, said settling time (dischargerate) of said at least one reference point and said sampling rate, andusing said threshold value in determining the validity of said pixelcoordinate estimates.
 102. A method of determining a touch screencoordinate for a touch screen comprising the steps of: turning on thedriver of the coordinate to be measured; measuring minimum, maximum, andraw position data for the coordinate being measured; and determining thecoordinate position as a function of the raw position in relation to acoordinate range.
 103. The method of claim 102 wherein the range isdetermined as a function of the difference between the minimum andmaximum position data.
 104. The method of claim 103 wherein thepositioning determining step includes subtracting the minimum positiondata from the raw position data.
 105. The method of claim 104 whereinthe raw, minimum and maximum position data are used to calibrate thetouch screen without requiring specific calibration using input. 106.The method of claim 104 including the further step of turning off thedriver of a coordinate not being measured.
 107. The method of claim 104wherein the foregoing steps are repeated for the other driver whosecoordinate is to be determined.
 108. An apparatus determining a touchscreen coordinate for a touch screen comprising: means for turning onthe driver of the coordinate to be measured; means for measuringminimum, maximum, and raw position data for the coordinate beingmeasured; and means for determining the coordinate position as afunction of the raw position in relation to a coordinate range.
 109. Theapparatus of claim 108 wherein the coordinate range is determined as afunction of the difference between the minimum and maximum positiondata.
 110. The apparatus of claim 109 wherein the positioningdetermining means includes means for subtracting the minimum positiondata from the raw position data.
 111. The apparatus of claim 110 whereinthe raw, minimum and maximum position data are used to calibrate thetouch screen without requiring specific calibration using input. 112.The apparatus of claim 110 further including means for turning off thedriver of a coordinate not being measured.
 113. A method of determiningwhether or not a touch screen has been touched comprising the steps of:providing an analog to digital converter which supplies an analog todigital reading; reading a minimum bit level; determining whether thereading is smaller than the minimum bit level; and determining theabsence of a user touch if the modified reading is less than the minimumbit level.
 114. The method of claim 113 wherein the reading stepincludes the use of a pull down resistor.
 115. Apparatus determiningwhether or not a touch screen has been touched comprising: means forproviding an analog to digital reading from an analog to digitalconverter; means for reading a minimum bit level; means for determiningwhether the reading is smaller than the minimum bit level; and means fordetermining the absence of a user touch if the reading is less than aminimum bit level.
 116. The apparatus of claim 115 wherein the providingmeans includes a pull down resistor.
 117. A method of speeding up thereading of analog to digital converter signals to a touch screencomprising the steps of: reading a first coordinate of a coordinate pairat a first time; consecutively reading the same coordinate at a secondtime; determining if the absolute value of the difference between thefirst coordinate and the consecutive coordinate is less than apredetermined value; and quantifying, responsive to the differencedetermining step the coordinate position as a function of the first orthe consecutive coordinate.
 118. The method of claim 117 wherein theconsecutive coordinate is used as the coordinate position.
 119. Themethod of claim 118 wherein the steps are repeated for the other desiredcoordinate position.
 120. Apparatus speeding up the reading of analog todigital converter signals to a touch screen comprising: means forreading a first coordinate of a coordinate pair at a first time; meansfor consecutively reading the same coordinate at a second time; meansfor determining if the absolute value of the difference between thefirst coordinate and the consecutive coordinate is less than apredetermined value; and means, response to the determining means, forquantifying the coordinate position as a function of the first or theconsecutive coordinate.
 121. The apparatus of claim 120 wherein theconsecutive coordinate is used as the coordinate position.
 122. A methodof determining whether or not a touch screen has been touched comprisingthe steps of: reading a first coordinate of a coordinate pair at a firsttime; consecutively reading the same coordinate at a second time;determining if the absolute value of the difference between the firstcoordinate and the consecutive coordinate is less than a predeterminedvalue; and quantifying, responsive to the difference determining stepthe coordinate position as a function of the first or the consecutivecoordinate.
 123. The method of claim 117 wherein the consecutivecoordinate is used as the coordinate position.
 124. The method of claim118 wherein the steps are repeated for the other desired coordinateposition.
 125. Apparatus determining whether a touch screen has beentouched comprising: means for reading a first coordinate of a coordinatepair at a first time; means for consecutively reading the samecoordinate at a second time; means for determining if the absolute valueof the difference between the first coordinate and the consecutivecoordinate is less than a predetermined value; and means, response tothe determining means, for quantifying the coordinate position as afunction of the first or the consecutive coordinate.
 126. The apparatusof claim 120 wherein the consecutive coordinate is used as thecoordinate position.
 127. A method of eliminating noise from the readingof analog to digital converter signals to a touch screen comprising thesteps of: reading a first coordinate of a coordinate pair at a firsttime; consecutively reading the same coordinate at a second time;determining if the absolute value of the difference between the firstcoordinate and the consecutive coordinate is less than a predeterminedvalue; and quantifying, responsive to the difference determining stepthe coordinate position as a function of the first or the consecutivecoordinate.
 128. The method of claim 117 wherein the consecutivecoordinate is used as the coordinate position.
 129. The method of claim118 wherein the steps are repeated for the other desired coordinateposition.
 130. Apparatus eliminating noise from the reading of analog todigital converter signals to a touch screen comprising: means forreading a first coordinate of a coordinate pair at a first time; meansfor consecutively reading the same coordinate at a second time; meansfor determining if the absolute value of the difference between thefirst coordinate and the consecutive coordinate is less than apredetermined value; and means, response to the determining means, forquantifying the coordinate position as a function of the first or theconsecutive coordinate.
 131. The apparatus of claim 120 wherein theconsecutive coordinate is used as the coordinate position.
 132. In atouch-screen display system for generating pixel coordinate estimatesresponsive to a user touching a display screen, an apparatus forenabling detection of a “no touch” state of said touch-screen displaysystem comprising: at least one bus bar; at least one driverelectrically connected to said at least one bus bar to selectivelyswitch said at least one bus bar between at least two of a plurality ofelectrical potentials wherein the at least one driver is selected tohave an off state impedance establishing a pre-determined dischargerate.
 133. In a touch-screen display system for generating pixelcoordinate estimates responsive to a user touching a display screen, anapparatus for enabling detection of a “no touch” state of saidtouch-screen display system comprising: at least one bus bar; at leastone driver electrically connected to said at least one bus bar toselectively switch said at least one bus bar between at least two of aplurality of electrical potentials wherein the at least one driver iscontrolled to establish pre-determined discharge rates.
 134. A method ofdetermining whether or not a touch screen has been touched comprisingthe steps of: providing an analog to digital converter which supplies ananalog to digital reading; reading a maximum bit level; determiningwhether the reading is smaller than the maximum bit level; anddetermining the absence of a user touch if the modified reading is lessthan the maximum bit level.
 135. The method of claim 113 wherein thereading step includes the use of a pull up resistor.
 136. Apparatusdetermining whether or not a touch screen has been touched comprising:means for providing an analog to digital reading from an analog todigital converter; means for reading a maximum bit level; means fordetermining whether the reading is smaller than the maximum bit level;and means for determining the absence of a user touch if the reading isless than a maximum bit level.
 137. The apparatus of claim 115 whereinthe providing means includes a pull up resistor.